Study On The LAGP Conducting Glass-ceramic

Li_1.5Al_0.5Ge_1.5（PO₄）₃（LAGP） lithium ionic conducting glass-ceramicscomposed of crystalline phase LiGe₂（PO₄）₃and the amorphous phase werefabricated by crystallization process.LAGP glass-ceramics are thought to be candidate electrolytes for all solid statelithium ionic secondary batteries because of their high lithium ionic conductivity,excellent mechanical strength and electrochemical stability. The paper reported theoptimization of glass composition, crystallization mechanism, microstructurecharacteristics and the electrical performance of LAGP glass-ceramics, whichprovides the theoretical basis for their further application in all-state lithium ionicbattery. The main results and new contributions were listed as follows:1. The crystallization kinetics of LAGP glass was studied by DifferentialScanning Calorimetry （DSC） under non-isothermal condition at different heatingrates. It was found that the activation energy of crystallization （E_c） values obtainedusing three different methods are in good agreement with each other in theexperimental errors, yielding451.69kJ/mol for the Kissinger equation,465.1kJ/molfor Augis-Bennett equation and442.01kJ/mol for Matusita equation. Tt indicatesthat the calculated value of E_cis credible, suggesting the crystallization behavior ofLAGP glass during crystallization. The value of Avrami index （n） LAGP glassobtained from Matusita’s equation is2.2, suggesting bulk crystallization duringtheir amorphous to crystalline transformation.2. The optimum heat treatment process of LAGP glass-ceramics, crystallized at 850℃for8h with the heating rate of3℃/min, was obtained by orthogonalexperiment. By this crystallization process, the SEM pictures of LAGP glass-ceramics showed presence of uniform crystals and dense microstructure.3. The highest conductivity (5.9×10^-4S/cm) at room temperature was obtainedfor the Li_1.5Al_0.5Ge_1.6（PO₄）₃glass-ceramic sheet specimen crystallized at850℃for8h with the heating rate of3℃/min. The effective compensation of GeO₂evaporatein high temperatures made the Li_1.5Al_0.5Ge_1.6（PO₄）₃glass-ceramic possessed finecrystalline grains, homogeneous microstructure and uniform distribution, whichbenefited the lithium ionic conductivity of the LAGP glass-ceramics.4. The bending strength of Li_1.5Al_0.5Ge_1.6（PO₄）₃glass-ceramic was82.24Mpa,strong enough to be used as electrolyte in lithium-ion battery. TheLi_1.5Al_0.5Ge_1.5（PO₄）₃glass-ceramic proved favorable electrochemical stabilityagainst lithium metal within one month and wide electrochemical window （0⁷V）,suggesting that it would be a promising electrolyte for practical application in all-solid-state lithium-ion batteries.Therefore it is very important in academic and practical significance toresearch and development of LAGP glass-ceramics, which provides valuableconclusions and benefits the future work.